This invention relates to intraocular lenses. In particular, the present invention relates to methods for determining whether intraocular lens materials have a propensity for preventing posterior capsule opacification.
Foldable intraocular lens (xe2x80x9cIOLxe2x80x9d) materials can generally be divided into three categories: silicone materials, hydrogel materials, and non-hydrogel acrylic materials. Many materials in each category are known. See, for example, Foldable Intraocular Lenses, Ed. Martin et al., Slack Incorporated, Thorofare, N.J. (1993). Biocompatibility varies among different IOL materials within and among each category. Although the distinction between hydrogel and non-hydrogel acrylic materials is sometimes unclear, for purposes of the present application, acrylic materials that absorb 5% (by weight) or less water at 37xc2x0 C. are considered non-hydrogel acrylic materials.
One measure of biocompatability for an IOL can be the incidence of posterior capsule opacification (xe2x80x9cPCOxe2x80x9d). A number or factors may be involved in causing and/or controlling PCO. For example, the design and edge sharpness of an IOL may be a factor. See, Nagamoto et al., J. Cataract Refract. Surg., 23:866-872 (1997); and Nagata et al., Jpn. J. Ophthalmol., 40:397-403 (1996). See, also, U.S. Pat. Nos. 5,549,670 and 5,693,094. Another factor appears to be the lens material itself. See, for example, Mandle, xe2x80x9cAcrylic lenses cause less posterior capsule opacification than PMMA, silicone IOLs,xe2x80x9d Ocular Surgery News, Vol. 14. No. 15, p. 23 (1996). See, also, Oshika, et al., xe2x80x9cTwo Year Clinical Study of a Soft Acrylic Intraocular Lens,xe2x80x9d J. Cataract. Refract. Surg., 22:104-109 (1996); and Ursell et al., xe2x80x9cRelationship Between Intraocular Lens Biomaterials and Posterior Capsule Opacification,xe2x80x9d J. Cataract Refract. Surg., 24:352-360 (1998).
One method of addressing the PCO problem involves administering a pharmaceutical agent to the capsular bag area at the time of, or immediately after, extracapsular cataract extraction. See, for example, U.S. Pat. No. 5,576,345 (pharmaceutical agent=the cytotoxic agent taxol or an ophthalmically acceptable derivative); U.S. Pat. Nos. 4,515,794; and 5,370,687. Alternatively, the pharmaceutical agent may be tethered to the surface of the IOL material. See, for example, U.S. Pat. No. 4,918,165. The pharmaceutical agents are intended to kill or prevent the growth of proliferating cells that might cause PCO or xe2x80x9csecondary cataracts.xe2x80x9d Yet another method involves the physical destruction or removal of lens epithelial cells. See, Saika et al., J. Cataract Refract. Surg., 23:1528-1531 (1997).
Another method of addressing PCO is the prophylactic laser therapy method disclosed in U.S. Pat. No. 5,733,276. According to this method, the lens capsule is irradiated with laser irradiation to destroy cells which remain in the lens capsule after extraction of a cataract.
Other methods theorized for reducing the risk of PCO involve adhering the posterior capsule to the IOL at the time of implantation, as in U.S. Pat. No. 5,002,571. According to the ""571 patent, a non-biological glue or, preferably, a biological glue, such as fibrin, collagen, or mussel glue, is used to adhere the posterior lens capsule to the posterior surface of an IOL. The glue may be applied over the entire posterior surface of the IOL or just as an annulus around the outer perimeter of the posterior surface of the IOL.
In contrast, U.S. Pat. No. 5,375,611 discloses a method of reducing the risk of PCO by preventing the adherence of the posterior capsule to the IOL. According to the ""611 patent, the posterior surface of the lens capsule itself is chemically modified at the time of extracapsular cataract extraction. The chemical modification is achieved by depositing a water-insoluble stable or permanent layer of a cell attachment preventing compound onto the posterior surface of the lens capsule. The stable or permanent layer may be a polymer, such as polyethylene glycol, polysaccharides, polyethylenepropylene glycol, and polyvinyl alcohols.
The present invention relates to a method of determining the propensity of an intraocular lens (xe2x80x9cIOLxe2x80x9d) material to prevent posterior capsule opacification (xe2x80x9cPCOxe2x80x9d). The method involves incubating replicate samples of an IOL material in a liquid composition comprising collagen IV for a time sufficient to allow at least some of the collagen IV to be adsorbed onto the surface of the IOL material, washing off any loosely bound collagen IV, and then determining for a first sample the amount of collagen IV that remains bound to the IOL material after washing. A second sample is further processed by subjecting it to a collagen IV desorption step and a second washing step. The amount of collagen IV that remains bound to the second sample of IOL material following the desorption and second washing steps is then determined and compared to the amount that remained bound to the first sample. The amount of collagen IV that remains bound after the desorption step can be considered to be specifically or permanently bound, in contrast to any amount of collagen IV that is only non-specifically or transiently bound to the IOL material.
The present invention also relates to IOL materials capable of permanently binding to collagen IV to an extent sufficient to allow an IOL posterior optic surface that contacts the posterior lens capsule to prevent PCO. Without intending to be bound by any theory, it is believed that IOL posterior surfaces that specifically and strongly bind to the lens capsule significantly reduce the risk of or prevent PCO.